1. Field of the Invention
This invention pertains generally to electrical connectors and specifically to interconnects between highly complex multichip modules that are densely loaded with thermally dissipative semiconductor dice.
2. Description of the Related Art
Prior to the present invention, modules were typically interconnected using a flexible film type connector. These connectors use a polymer film or tape, typically of a material such as Kapton, as a compliant carrier for metallizations. The metallizations serve as electrical connectors that may be soldered or otherwise interconnected to the connection sites on the modules.
During the operation of a multichip module, there may be substantial thermal energy dissipated through the exterior of the package. This thermal energy is often the source for localized heating that leads to thermally induced expansion. When a component such as the module expands from internal heating, another structure, even if of matched thermal expansion coefficient, will not expand in a matching way. If a rigid material such as glass or alumina is incorporated as a connector, the electrical connections and possibly the connector and the device are prone to failure.
The use of a polymer material is necessitated by the need for a carrier that will deform when forces are applied. This deformation serves to protect the module, connector, and solder joints from thermal stress induced failures. Polymers such as Kapton are particularly prevalent for these types of connectors because of good thermal and chemical resistance and availability.
However, polymer materials do not possess good thermal conductivity. In fact, they are the worst thermal conductors available. Unfortunately then, the use of a flexible connector results in a sacrifice of thermal dissipation which will accelerate the failure of the circuitry contained within the multichip module.
In order to provide adequate cooling for the modules, other structures have been proposed. On such structure utilizes metal pins placed in a grid pattern to interconnect the devices. An electrically non-conductive fluid such as air or Freon may then be circulated between the modules to provide enhanced cooling.
Unfortunately, the use of metal pins requires complex assembly and production, resulting in greater cost. Bent pins result during production, further affecting the final cost. Additionally, since the metal pins require a certain amount of length to yield sufficiently, space is sacrificed.
In summary, to date there has not been an adequate solution to the interconnection of multichip modules that addresses thermal dissipation, expansion, cooling, environmental resistance including resistance to chemical attack, and package durability.